## Create an image, and add something to it
docker build -t myimage:latest -<<EOF
FROM alpine
RUN apk add curl
EOF
## Save the image
docker save myimage:latest -o myimage.tar
## Create a systemd-extension from the image
## oci2sysext <image-tar-path> <sysext-name>
oci2sysext myimage.tar myimage
## Install the systemd-extension
mv myimage.raw /var/lib/extensions
# or symlinking
# mkdir extensions
# mv myimage.raw extensions/
# sudo ln -s $PWD/extensions /var/lib/extensions/